Hydrocracking process utilizing group VIII metal/alumina catalysts activated with hydrogen halide/halosilane/organic halide

ABSTRACT

A catalyst comprising a Group VIII metal selected from Pt, Ir, Os, Ru, Rh, or Pd supported on alumina is activated at an elevated temperature with an activating gas comprising a hydrogen halide such as HCl, a halosilane such as silicon tetrachloride, and an organic halide such as ethyl chloride. The resulting catalysts exhibit an outstandingly high isomerization rate constant in the isomerization of feedstocks such as n-butane to isobutane. These catalysts are also suitable for hydrocracking operations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser.No. 681,933, filed Apr. 30, l976, which in turn is a divisional ofcopending application Ser. No. 546,820, filed Feb. 3, l975, now U.S.Pat. No. 3,979,333.

BACKGROUND OF THE INVENTION

This invention relates to activating catalysts of selected Group VIIImetals on alumina.

Platinum supported on alumina has long been used as an isomerizationcatalyst. It is broadly known to treat such materials with halogens toactivate same. Myers, U.S. Pat. No. 3,449,264 issued June 10, l969,broadly discloses activation utilizing certain halogens and/or halidessuch as HCl for activating alumina catalysts.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a hydrocarbon conversioncatalyst of improved activity;

IT IS A FURTHER OBJECT OF THIS INVENTION TO PROVIDE A PROCESS FORACTIVATING A PLATINUM GROUP METAL/ALUMINA CATALYST UTILIZING ACOMBINATION OF A HALOSILANE AND AN ORGANIC HALIDE;

IT IS YET A FURTHER OBJECT OF THIS INVENTION TO PROVIDE A PLATINUM GROUPMETAL/ALUMINA CATALYST WHICH IS APPLICABLE TO COMMERCIAL SCALEOPERATION; AND

IT IS YET A FURTHER OBJECT OF THIS INVENTION TO PROVIDE A CATALYSTCAPABLE OF EFFECTING ISOMERIZATION AT A HIGHER RATE CONSTANT.

In accordance with this invention a catalyst of Pt, Ir, Os, Ru, Rh, orPd on alumina is activated in the presence of a hydrogen halide selectedfrom hydrogen chloride and hydrogen bromide in combination with ahalosilane selected from chlorosilanes and bromosilanes and an organichalide selected from organic chlorides and organic bromides.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The catalysts which are activated in accordance with this invention arebasically a selected Group VIII metal supported on an active aluminabase. The applicable Group VIII metals are at least one of platinum,iridium, osmium, palladium, rhodium, and ruthenium. This class ofcatalyst is well known in the prior art and generally contains from 0.01to 10, preferably 0.1 to 1, weight percent metal based on the totalcatalyst weight including the alumina base. The preferred metal isplatinum. These catalysts can also contain minor amounts of a halogenincorporated during preparation of the catalyst, chlorine being thehalogen most commonly present. Although one or both of these halogenscan be present in the catalyst prior to activation by the process of thepresent invention, the catalyst containing them is not the equivalent ofa catalyst which has been activated by the present process. The amountof halogen in the catalyst as prepared (i.e., prior to activation inaccordance with this invention) if any, is usually less than about 1.5weight percent based on the total weight of the catalyst.

To produce these catalysts, an alumina, well known in the art as an"active" alumina is essential. Active aluminas may be syntheticallyprepared as by calcination of alumina gels which are formed by addingsuch reagents as ammonium hydroxide to a salt of aluminum, such asaluminum chloride or aluminum nitrate. These aluminas are generallygamma or eta aluminas depending upon the dehydrating conditions used.Similar active aluminas may be prepared by calcination of naturallyoccurring aluminas such as the monohydrate and the trihydrate. Bauxiteis a common source of active alumina when properly calcined anddehydrated. The alumina base of the catalyst may contain minor amountsof silica and boron oxide. The amounts of these materials should be lessthan about 30 percent, preferably less than about 10 weight percent ofthe catalyst base component to produce the most active catalyst.

The hydrogen halide is HCl or HBr, most preferably anhydrous HCl.

The halosilane is preferably a chlorosilane, which can be represented bythe formula SiX₄ in which each X can be the same or different and whereat least one X is chlorine and the other X substituents are selectedfrom the group consisting of chlorine, hydrogen, and alkyl radicalscontaining from 1 to 3 carbon atoms per molecule. Exemplary compoundsinclude silicon tetrachloride, trichlorosilane, monochlorosilane,trichloromethylsilane, dichloropropylsilane and the like. A presentlypreferred compound based on cost and availability is silicontetrachloride. The corresponding bromosilanes can also be used.

When a hydrogen halide is used in the activating gas along with ahalosilane, it is preferred that the halogens in each compound be thesame. That is, a combination consisting of silicon tetrachloride andhydrogen chloride is preferred rather than silicon tetrachloride andhydrogen bromide, for example.

The organic halide is preferably a chlorinated paraffin containing from1 to 3 carbon atoms per molecule. Exemplary compounds include methylenechloride, ethyl chloride, isopropyl chloride, chloroform, carbontetrachloride, and the like. The corresponding bromine compounds canalso be used.

The Pt, Ir, Os, Ru, Rh, or Pd metal on alumina catalyst is firstcalcined in a manner known in the art, for instance, by heating to atemperature within the range of 500° to 900° F., more preferably 700° to900° F., for a time within the range of 1 to 10, preferably 1 to 3,hours. Preferably, this is carried out in the presence of air althoughair is not essential.

The catalyst is then heated to the activation temperature which isgenerally within the range of 500°to l600° F., preferably 900° to 1500°F., still more preferably 1200° to 1500° F. The catalyst may then beheld within this temperature range for a time of at least 10 minutes,preferably at least 1 hour. A range of 1.5 to 15, more preferably 1.5 to5, hours is satisfactory. This step of holding the catalyst atactivation temperature is primarily for the purpose of being sure thecatalyst is dry.

The catalyst is then treated with a dry activating gas comprising thehydrogen halide plus the combination of a halosilane and an organichalide. The temperature during this treatment is still within the samerange of 500° to 1600°, preferably 900° to 1500°, more preferably 1200°to 1500°F. Time for this treatment is normally within the range of 0.1to 10, preferably 1 to 3, hours. After this treatment, thethus-activated catalyst is cooled, for instance, to ambient temperature.The heating, holding at activation temperature, activation, and coolingcan be carried out in an inert atmosphere such as under nitrogen, ormore preferably in the presence of hydrogen. A mixture of nitrogen andhydrogen can be utilized or pure hydrogen. Preferably a small amount ofhydrogen halide, i.e. 1-20 mole percent, is added to the nitrogen,hydrogen, or hydrogen-nitrogen mixture during cooling.

The concentration of the halosilane and the organic halide in theactivating ambient are preferably in the range of about 0.05 to about 10weight percent each of the halosilane and organic halide based on theweight of the hydrogen halide. A more preferred range is about 0.1 toabout 5 weight percent each. The weight ratio of the halosilane to theorganic halide can be within the range of 0.1:1 to 10:1. A relativelyhigh ratio of the organic halide is preferred since one very beneficialaspect of the invention is the ability to achieve improved results withonly a small amount of halosilane (thus reducing any silicon deposit onthe catalyst) by utilizing a mixture of the halosilane and the organichalide. Good results have been obtained when the weight ratio ofhalosilane to organic halide ranges from about 0.3:1 to about 1:1.

As noted hereinabove, hydrogen is preferably present during theactivation step at least. In instances where hydrogen is present, it canbe present in an amount within the range of 1 to 95 mole percent basedon the moles of hydrogen halide.

The activating ambient is contacted with the catalyst in an amounteffective to increase the halogen content of the catalyst and toincrease the activity of the catalyst. The amount of halogenincorporated by this technique will generally be within the range of 1to 10, preferably 2 to 6, weight percent based on the weight of theGroup VIII metal-alumina composite.

The catalysts of the present invention are particularly applicable tothe skeletal isomerization of isomerizable hydrocarbons includingacyclic paraffins, and naphthenes. These catalysts are particularlysuitable for the isomerization of straight chain or singly-branchedparaffins containing four to eight carbon atoms per molecule includingn-butane, n-pentane, n-heptane, methylpentane, and the like. Someexamples of naphthenes which can be isomerized with these catalysts aremethylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, and the like. Actually, these are equilibriumreactions as follows:

    cyclohexane ⃡ methylcyclopentane

    methylcyclohexane ⃡ dimethylcyclopentane

    pentane ⃡ methylbutane

    n-hexane ⃡ methylpentanes ⃡ dimethylbutanes

Conditions can be adjusted to give hydrocracking, as for instance toproduce butane from n-octane. Preferred process conditions forhydrocracking are as follows. Pressure: 50-5000 psig, preferably100-3000 psig; temperature: 200°-800° F., preferably 300°-700° F.;liquid hourly space velocity: 0.1-30, preferably 0.5-20; and H₂/hydrocarbon mole ratio: 0.5-30, preferably 2-20. Applicable feedsinclude C₅ and higher boiling hydrocarbons such as naphthas anddistillates. The catalyst is especially useful in hydrocracking toproduce C₄ and lighter hydrocarbons. Feeds should be substantially freeof poisons such as water, oxygen-containing organic compounds and sulfurcompounds.

The isomerization reaction conditions and recovery procedures can bevaried to achieve the desired conversion in a manner known in the art.Isomerization of normal butane to isobutane is one presently preferredapplication.

Hydrocarbons to be isomerized are contacted with the activated catalystsprepared in accordance with the invention at an isomerizationtemperature of about 100°-600° F., more preferably 150°-450° F., in thepresence of free hydrogen. The hydrogen-hydrocarbon mol ratios normallyused during isomerization are within the range of about 0.25 to 10 toinsure long catalyst life. Liquid hourly space velocities, i.e., thevolume of liquid charge per hour per volume of catalyst, of about 0.1 to15 are satisfactory and pressures within the range of atmospheric to1500 psig in the isomerization zone are suitable.

Maintenance of catalyst activity during the isomerization process isaided by the inclusion of 0.001 to about 1 weight percent chloride inthe feed in the form of chlorinated hydrocarbon promoters such as carbontetrachloride, chloroform, ethyl chloride, isopropyl chloride, etc. Thisis not a substitute for the activation of the catalyst but it aids inmaintaining over long process periods the high level of activity of theinvention catalysts.

The isomerization process can be carried out either in a batchwise orcontinuous basis, preferably the latter. In a continuous process it isto be understood that hydrogen in the effluent product can be separatedand recycled and that recycling of isomerization promoters, if employed,can be practiced. These catalysts are also suitable for hydrocrackingoperations.

EXAMPLE

A gamma-alumina in the form of 1/16 inch diameter extrudate wasimpregnated with an aqueous solution of chloroplatinic acid andhydrochloric acid sufficient to give a platinum content of 0.37 weightpercent and a chloride content of 1.25 weight percent based on thecalcined composite. The impregnated sample was dried in air at 240° F.and calcined in air at 800° F. for 2 hours. Equal portions by weightwere taken from the calcined catalyst and each portion was heated fortwo hours in a hydrogen atmosphere followed by activation at about 1250°F. in the medium chosen for 2 hours as shown in the Table. Afteractivation each catalyst was removed from the furnace in its quartztube, cooled in the activating ambient to about 200° F. (12-13 minutes)and transferred to a reactor for testing. The isomerization tests wereconducted at about 305°-325° F. at a space velocity of 4 parts liquidfeed per part catalyst per hour (by volume, LHSV), 500 psig and a 0.5hydrogen/feed mole ratio. The feed tested was n-butane containing about200 ppm chloride as carbon tetrachloride. The results are presented inthe Table.

                  TABLE                                                           ______________________________________                                        Effect on Promoting Halide-Containing Compounds                               On Isomerization Activity of Treated Catalysts                                                  Isomerization                                               Promoter Added To.sup.(a)                                                                       Results at 305-325° F.                               Run  HCI--H.sub.2 Activating                                                                        Isobutane in C.sub.4                                                                      Relative.sup.(b)                            No.  Gas. Wt. % of HCl                                                                              Effluent Mole %                                                                           Rate Constant                               ______________________________________                                        1    None             53.3        1.09                                        2    1.2 SiCl.sub.4   58.0        1.40                                        3    2.8 SiCl.sub.4   58.0        1.40                                        4    1.9 ethyl chloride                                                                             57.4        1.36                                        5    3.8 ethyl chloride                                                                             56.7        1.30                                        6    0.2 SiCl.sub.4 + 1.1 ethyl                                                                     56.8        1.31                                             chloride                                                                 7    0.4 SiCl.sub.4 + 1.1 ethyl                                                                     59.3        1.52                                             chloride                                                                 8    0.9 SiCl.sub.4 + 1.1 ethyl                                                                     58.7        1.47                                             chloride                                                                 9    ≅0.7 SiCl.sub.4.sup.(c) + 1.9 ethyl                                                  60.6        1.67                                             chloride                                                                 10   0.7 SiCl.sub.4 + 1.9 ethyl                                                                     58.3        1.43                                             chloride                                                                 ______________________________________                                         .sup.(a) Unpromoted ambient consisted of 62 mole percent HCl and 38 mole      percent H.sub.2. The activation gas flow was 29 liters per hour at STP.       The SiCl.sub.4 was added by passing a portion of the H.sub.2 through the      silicon tetrahalide. The ethyl chloride was metered into the gas stream b     means of a rotameter.                                                         .sup.(b) Calculated from the test results using the first order reversibl     reaction kinetic equations presented on pages 62-63 of "Chemical Reaction     Engineering" Levenspiel, John Wiley & Sons, 1962, Library of Congress         Catalog No. 62-15185.                                                         .sup.(c) Less precise balance used in weighing. The actual amount is          believed to be between about 0.4 and 0.7 weight percent.                 

Inspection of the results shows that the isomerization activity of thecatalyst is improved when small amounts of silicon tetrachloride orethyl chloride are present in the activating gas along with hydrogenchloride. Run 5 suggests that about 4 weight percent ethyl chloride issomewhat less effective than the about 2 weight percent used in Run 4.The combinations of silicon tetrachloride and ethyl chloride shown inRuns 6-10 are generally more effective than about equal weights ofeither component alone when the amount of silicon tetrachloride exceedsabout 0.2 weight percent.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

What is claimed is:
 1. A hydrocarbon conversion process which comprises contacting a hydrocarbon under hydrocracking conditions with a catalyst produced by:heating an alumina supported Pt, Ir, Os, Ru, Rh, or Pd metal catalyst at a temperature within the range of 500° to 1600° F.; contacting said catalyst at said temperature of 500° to 1600° F. with a dry activating gas comprising a hydrogen halide selected from the group consisting of HC1 and HBr, a halosilane selected from the group consisting of chlorosilanes and bromosilanes, and an organic halide selected from the group consisting of organic chlorides and organic bromides; and thereafter cooling the thus-contacted catalyst.
 2. A process according to claim 1 wherein said feed is a C₅ or higher boiling hydrocarbon.
 3. A process according to claim 1 wherein said feed is n-octane and wherein said n-octane is converted to butane.
 4. A process according to claim 1 wherein said hydrocracking conditions are: pressure, 100-3000 psig; temperature, 300°-700° F., liquid hourly space velocity, 0.5-20 and H₂ /hydrocarbon mole ratio 2-20.
 5. A method according to claim 4 wherein said organic chlorides are chlorinated paraffins and said organic bromides are brominated paraffins and wherein a weight ratio of halosilane to said organic halide is within the range of 0.1:1 to 10:1.
 6. A method according to claim 1 wherein said organic chlorides are chlorinated paraffins and said organic bromides are brominated paraffins and wherein a weight ratio of halosilane to said organic halide is within the range of 0.1:1 to 10:1.
 7. A method according to claim 1 wherein said temperature for contacting said catalyst with said activating gas is within the range of 1200° to 1500° F. and said contacting of said catalyst is carried out for a time within the range of 0.1 to 10 hours and wherein said hydrogen halide is anhydrous hydrogen chloride, said halosilane is a chlorosilane of the formula SiX₄ in which each X can be the same or different and wherein at least one X is chlorine and the other X substituents are selected from the group consisting of chlorine, hydrogen, and alkyl radicals containing from 1 to 3 carbon atoms per molecule and said organic halide is a chlorinated paraffin containing from 1 to 3 carbon atoms per molecule.
 8. A method according to claim 7 wherein said metal is platinum and is present in an amount within the range of 0.1 to 1 weight percent based on the weight of said catalyst, said halosilane is silicon tetrachloride, said organic halide is ethyl chloride, and said activating gas is carried by a stream of hydrogen. 